1. Field of the Invention
The present invention relates to an amplifier circuit for outputting an input signal at a specific output impedance, and in particular, to an amplifier circuit that is built in a video camera and the like and is used for amplifying a video signal and the like.
2. Description of Related Art
Conventionally, since an output impedance is specified at 75 ohms in an amplifier circuit for outputting a video signal, the amplifier circuit outputs a signal through a resistor of 75 ohms by driving the signal in a low-impedance output amplifier circuit, the signal being twice as large as a signal at a 75-ohm terminating resistor.
Nevertheless, it is necessary for the conventional amplifier circuit to output a signal of 2 Vpp in the low-impedance output amplifier circuit so as to output a video signal having an amplitude of 1 Vpp. Therefore, a supply voltage of at least 4 V is required if the low-impedance output amplifier circuit is to be constructed of a push-pull circuit with bipolar transistors.
In addition, if the low-impedance output amplifier circuit is constructed in a collector-output type, it is possible to lower the supply voltage to a degree. Nevertheless, it is difficult to operate the low-impedance output amplifier circuit at the supply voltage of 3 V.
Recently, supply voltages have been reduced so as to get longer battery lives in portable apparatuses, with the operation of 3 volt power supplies also being requested in video cameras. Nevertheless, it is not possible for the conventional art to correspond to these requirements.